I'm currently running Windows 8 Pro (64 bit). I have 8gb of ram...and for some weird reason every so often I boot into windows and I get something like the picture shown above. On several cases it's gone even higher (95-98% usage)

This seems like a memory leak to me...but I have no clue how to fix it. Tried reinstalling windows, but the issue persists!

Well the first thing you are going to have to do is make sure that windows is actually recognizing all of your memory at every boot (I find that ~75% memory usage sometimes and ~100% memory usage other times to be a bit fishy), and then make sure that it actually is superfetch using the memory, which means you are going to have to look through all of the running processes, not just the ones that are running under your user account.

There has to be something you're running or have configured that is doing this. My Win8 laptop with a few Chrome tabs open is using 50% of 4GB memory (38% with browser closed) and my Win7 desktop with more stuff running but 16GB RAM is at 23% right now. Have you disabled your pagefile or something?

the disk cache will only store files that have been read during the current session. it will not preemptively start caching files on its own. so my guess is that you only accessed 9 gb of files during your session.

windows may also leave a bit of memory free. since i posted the screenshot i used the system, havent rebooted, and free memory is now at 350 mb